1. Field of the Invention
This invention relates generally to local area networks (LANs) and more particularly to apparatus and to a method for determining the location of a network node or component from the interaction of the network node or component with the local area network.
2. Description of the Related Art
For certain local area networks, such as networks using the Carrier Sense Multiple Access/Collision Detect (CSMA/CD) architecture, as defined by the IEEE 802.3, a multiplicity of devices can be coupled to a (cable) segment of the local area network. For example, a segment can consist of a coaxial cable segment 500 meters in length. A local area network can include a plurality of cable segments, each cable segment coupled by a repeater unit (to compensate for losses experienced by signal propagation along the cable) to other cable segments and having up to 1024 system members coupled thereto. The system members are coupled to the coaxial cable by means of a device typically referred to as a tap. The tap is a unit that clamps onto the coaxial cable, pushes aside the braided grounding wire, and forces a small pin into the central conducting element to detect signals transmitted on the central conducting element. Referring now to FIG. 1, the typical configuration of a device coupled to the cable segment is shown. The tap and transceiver unit 12 are coupled to the coaxial cable segment 11. The tap portion physically couples to cable segment 11, while the transceiver portion encodes signals that are going to be applied to the cable segment 11 in the specified local area network format and decodes signals received from the cable segment 11. The network interconnect unit 14 is coupled to the tap and transceiver unit 12 and provides the data link protocols specific to the local area network. The network interconnect unit 14 typically provides power for the tap and transceiver unit 12 through the same conducting leads that carry the signals. The network interconnect unit 14 is typically contained within a data processing system 15, the data processing system typically referred to as a network node.
In the related U.S. patent application 07/076,724, a technique is disclosed for determining voltage levels of signals on the cable segment of the local area network. Because no technique has been available for calibrating the measured voltage levels, performance characteristics were inferred from comparing the measured signals as a function of time. However, the more reliable technique for determining operating characteristics is to determine the actual value of the network signals. It is the signal values or levels themselves that determine when the network activity is not within specifications.
A need has been felt for a technique to measure the actual voltage level of signals applied to the network rather than rely on time dependent changes in voltage levels to infer a deterioration of network operating conditions.